β-Sn晶粒取向及温度对Cu/SAC305/Cu微焊点时效界面反应的影响

为了探究不同等温时效温度下β-Sn晶粒取向及晶界特征对界面反应的影响,采用准原位观测手段对不同Sn取向的Cu/Sn3.0Ag0.5Cu/Cu(Cu/SAC305/Cu)微焊点进行研究. 结果表明,在不同温度下时效时,微焊点两侧界面IMC(Cu₆Sn₅ + Cu₃Sn两相)自始至终呈现对称性生长,表明时效过程中β-Sn晶粒取向及晶界的存在不会影响界面反应. 但是随着时效温度的升高,界面IMC的形貌和厚度发生明显变化. 在100 ℃时效后,界面处生成扇贝状的Cu₆Sn₅和较薄的不连续的Cu₃Sn层;在125 ℃时效后,界面处生成扇贝状的Cu₆Sn₅和较薄的连续的Cu₃Sn层;而在150 ℃时效后,界面IMC由层状Cu₆Sn₅和层状Cu₃Sn双层结构组成. 时效温度的升高促使Cu和Sn原子扩散加快,促进了扇贝状Cu₆Sn₅向层状转变并造成Cu₃Sn的快速生长. 同时,基于界面IMC厚度随时效时间的演变规律,获得了不同时效温度下微焊点界面IMC生长曲线,可为Sn基微焊点的可靠性评价提供依据.     

基于纳米压痕法分析无铅焊点内Cu6Sn5金属化合物的力学性能

采用纳米压痕技术对微电子封装中无铅焊点内界面化合物（IMC）Cu₆Sn₅的弹性模量和硬度进行了测试。根据实际工业工艺流程和服役工况,制备接近真实服役状态下的微电子封装中无铅焊点界面化合物试样;采用扫描电镜（SEM）和能量色散X射线荧光光谱仪（EDX）确定IMC的形貌和化学成分;利用连续刚度测量（CSM）技术,采用不同的加载速率对无铅焊点（Sn3.0Ag0.5Cu、Sn0.7Cu和Sn3.5Ag）内的界面化合物Cu₆Sn₅进行测量,得到载荷、硬度和弹性模量-位移曲线。根据纳米压痕结果确定Cu₆Sn₅的蠕变应力指数。     

电子封装中Cu/Sn/Cu焊点组织演变及温度对IMC立体形貌影响

通过电镀的方法在抛磨好的铜基体沉积4 μm的锡层,并组合成一个Cu/Sn/Cu结构.分别选择240℃、1 N作为钎焊温度和钎焊压力,在不同的钎焊时间下制备焊点,分析了Cu/Sn/Cu焊点组织演变规律.分别制备了不同钎焊温度下（240,270,300℃） Cu₆Sn₅和Cu₃Sn的立体形貌,分析了温度对Cu₆Sn₅和Cu₃Sn立体形貌的影响规律.结果表明,钎焊30 min后Cu₆Sn₅为平面状,随着钎焊时间的增加逐渐转变成扇贝状.在扇贝底部的Cu₃Sn要比扇贝两侧底部的Cu₃Sn厚.增加钎焊时间锡不断被反应,上下两侧Cu₆Sn₅连成一个整体.继续增加钎焊时间Cu₆Sn₅不断转变成为Cu₃Sn.随着钎焊温度的升高Cu₆Sn₅的立体形貌逐渐由多面体状转变成匍匐状,而Cu₃Sn晶粒随着钎焊温度上升不断减小.     

微小互连Cu-Sn界面钎焊及接头剪切行为

针对Cu-Sn-Cu三明治结构,进行0.06 MPa恒压钎焊. 基于Cu-Sn二元相图,选定了不同的钎焊温度与钎焊时间. 钎焊完成后,根据不同相组成可将接头分为残余锡,Cu₃Sn-Cu₆Sn₅-Cu₃Sn,Cu-Cu₃Sn-Cu三类. 为研究三种不同相组成接头抗剪强度之间的关系,进行1 mm/min加载速率的剪切试验,并对断口进行形貌分析. 结果表明,随着Sn与Cu₆Sn₅相继耗尽,接头抗剪强度不断升高. 残余锡接头,Cu₃Sn-Cu₆Sn₅-Cu₃Sn接头,Cu-Cu₃Sn-Cu接头抗剪强度分别为23.26,33.59,51.83 MPa. 分析断口形貌发现,在残余Sn接头断口中,可以分辨出Sn,Cu₆Sn₅,Cu₃Sn形貌,说明其断裂路径穿过了Cu₆Sn₅与Cu₃Sn两相. 在Cu₃Sn-Cu₆Sn₅-Cu₃Sn接头断口中,可分辨出Cu₆Sn₅,Cu₃Sn形貌,其断裂路径穿过了Cu₃Sn相. 全Cu₃Sn相接头断口中仅可分辨出Cu₃Sn相断裂形貌.     

基于原位观察Sn-3.0Ag-0.5Cu/Cu钎焊接头110℃时效过程中的显微结构

基于自制原位观察装置,研究了Sn-3.0Ag-0.5Cu/Cu焊点在110℃恒温时效下,0~168 h不同时效时间界面金属间化合物(IMC)的微观形貌和生长变化规律.结果表明,随着时效时间的延长,界面IMC(Cu₆Sn₅和Cu₃Sn)的厚度在不断增加;同时IMC的生长具有三维特性;随着时效时间的延长,Cu₆Sn₅在纵向方向上变化比较明显,高度是逐渐降低的;而在横向方向上变化较慢.SEM研究发现,时效过程中界面IMC的形貌由扇贝状转变成较为平整的层状,并出现分层现象.     

Ni含量对304/Sn-8Sb-4Cu-xNi/304钎焊接头组织与剪切性能的影响

研究了Ni含量对Sn-8Sb-4Cu-xNi(x=0, 0.5, 1和2,质量分数)钎料熔点和微观组织的影响,用Sn-8Sb-4CuxNi钎料对304不锈钢进行钎焊连接,分析了接头的界面组织与剪切性能.结果表明,添加不同含量的Ni后,Sn-8Sb-4Cu-xNi均为近共晶钎料,其熔点约为245℃;Sn-8Sb-4Cu钎料组织由α相基体、Sb₂Sn₃+Cu₆Sn₅+Sn复合相和Cu₆(Sn,Sb)₅相组成.添加Ni元素后,钎料中块状Cu₆(Sn,Sb)₅转变为细小、均匀分布的(Cu,Ni)₆(Sn,Sb)₅.当Ni含量小于1%时,随Ni含量的增加,钎料中的复合相和(Cu,Ni)₆(Sn,Sb)₅相均增加;当Ni含量为2%时,钎料中的复合相和(Cu,Ni)₆(Sn,Sb)₅相均减少,但(...     

电迁移对Ni/Sn3.0Ag0.5Cu/Cu焊点界面反应的影响

研究了温度为150℃,电流密度为5.0×10³A/cm²的条件下电迁移对Ni/Sn3.0Ag0.5Cu/Cu焊点界面反应的影响.回流焊后在Sn3.0Ag0.5Cu/Ni和Sn3.0Ag0.5Cu/Cu的界面上均形成了（Cu,Ni）₆Sn₅型化合物.时效过程中界面化合物随时效时间增加而增厚,时效800 h后两端的化合物并没有发生转变,仍为（Cu,Ni）₆Sn₅型.电流方向对Cu基板的消耗起着决定作用.当电子从基板端流向芯片端时,电流导致基板端Cu焊盘发生局部快速溶解,并导致裂纹在Sn3.0Ag0.5Cu/（Cu,Ni）₆Sn₅界面产生,溶解到钎料中的Cu原子在钎料中沿着电子运动的方向向阳极扩散,并与钎料中的Sn原子发生反应生成大量的Cu₆Sn₅化合物颗粒.当电子从芯片端流向基板端时,芯片端Ni UBM层没有发生明显的溶解,在靠近阳极界面处的钎料中有少量的Cu₆Sn₅化合物颗粒生成,电迁移800 h后焊点仍保持完好.电迁移过程中无论电子的运动方向如何,均促进了阳极界面处（Cu,Ni）₆Sn₅的生长,阳极界面IMC厚度明显大于阴极界面IMC的厚度.与Ni相比,当Cu作为阴极时焊点更容易在电迁移作用下失效.     

Cu基板退火处理的Cu/Sn58Bi/Cu钎焊接头界面微结构

研究了铜基板退火处理对Cu/Sn58Bi界面微结构的影响. 结果表明,在回流以及时效24 h后Cu/Sn58Bi/Cu界面只观察到Cu₆Sn₅. 随着时效时间的增加,在界面形成了Cu₆Sn₅和Cu₃Sn的双金属间化合物(IMC)层,并且IMC层厚度也随之增加. 长时间时效过程中,在未退火处理的铜基板界面产生了较多铋偏析,而在退火处理的铜基板界面较少产生铋偏析. 比较退火处理以及未退火处理的铜基板与钎料界面IMC层生长速率常数,发现铜基板退火处理能减缓IMC层生长,主要归因于对铜基板进行退火处理能够有效的消除铜基板的内应力与组织缺陷,从而减缓Cu原子的扩散,起到减缓IMC生长的作用.     

BGA焊点SAC305/ENEPIG/Cu界面反应演化及力学性能的尺寸效应

将直径为300、500和760μm的SAC305(Sn3.0Ag0.5Cu)焊球在ENEPIG/Cu焊盘上进行3次回流焊形成SAC305/ENEPIG/Cu焊点，并在185℃对焊点进行了时效(0～1000 h)处理，研究了焊球直径对回流及时效后微焊点界面金属间化合物(IMC)反应和演变的影响，分析了不同焊球直径的焊点在不同剪切速率下(0.2和20 mm/s)的剪切强度与断裂模式。结果表明：随焊球直径减小和时效时间延长，焊点界面金属间化合物(IMC)由单相(Cu, Ni)₆Sn₅向(Ni, Cu)₃Sn₄和(Cu, Ni)₆Sn₅两相演化，IMC生长速率随焊点尺寸的增大而减小，表现出明显尺寸效应；焊点剪切强度随剪切速率减小和时效时间增加而降低，且大尺寸焊点剪切强度的下降程度明显弱于小尺寸焊点，在高速(20 mm/s)剪切条件下，所有尺寸焊点时效300 h后断面均呈韧性断裂。     

快速热冲击下SAC305/Cu焊点氧化行为与金属间化合物生长动力学（英文）

通过电磁感应加热装置，研究SAC305/Cu焊点氧化行为和界面金属间化合物(IMC)生长动力学。结果表明，快速热冲击下焊点自身氧化行为是主要因素，内部的Cu₆Sn₅IMC会加剧焊点的氧化。Cu₆Sn₅层的生长由晶界扩散控制，Cu₃Sn层的生长则由体扩散控制。基底溶解的Cu原子主要扩散到界面IMC和焊料的内部。在快速热冲击下，焊点剪切强度大幅度降低，72 h后下降49.2%。断裂机制由韧性断裂向韧脆性混合断裂转变，最终转变为脆性断裂。     

Growth Behavior of Intermetallic Compounds at SnAgCu/Ni and Cu Interfaces

The growth behavior of reaction-formed intermetallic compounds (IMCs) at Sn3.5Ag0.5Cu/Ni and Cu interfaces under thermal-shear cycling conditions was investigated. The results show that the morphology of (Cu _x Ni_1–x )₆Sn₅ and Cu₆Sn₅ IMCs formed both at Sn3.5Ag0.5Cu/Ni and Cu interfaces gradually changed from scallop-like to chunk-like, and different IMC thicknesses developed with increasing thermal-shear cycling time. Furthermore, Cu₆Sn₅ IMC growth rate at the Sn3.5Ag0.5Cu/Cu interface was higher than that of (Cu _x Ni_1–x )₆Sn₅ IMC under thermal-shear cycling. Compared to isothermal aging, thermal-shear cycling led to only one Cu₆Sn₅ layer at the interface between SnAgCu solder and Cu substrate after 720 cycles. Moreover, Ag₃Sn IMC was dispersed uniformly in the solder after reflow. The planar Ag₃Sn formed near the interface changed remarkably and merged together to large platelets with increasing cycles. The mechanism of formation of Cu₆Sn₅, (Cu _x Ni_1–x )₆Sn₅ and Ag₃Sn IMCs during thermal-shear cycling process was investigated.     

Cu6Sn5和Ni3Sn4结构性能的第一原理计算

基于密度泛函理论的第一原理,计算了锡基无铅焊点界面常见的金属间化合物Cu6Sn5和Ni3Sn4的平衡晶格常数、合金形成焓以及弹性常数,分析了结构稳定的电子机制.结果表明,Cu6Sn5较Ni3Sn4合金形成能负,因此Cu6Sn5在热力学上更稳定,其合金化能力也较强.在力学性能方面,两相均属脆性相,表现出弹性各向异性,而Ni3Sn4的键合作用较强,弹性模量、剪切模量均大于Cu6Sn5,但Cu6Sn5表现出更好的塑性.从电子结构的角度,Cu6Sn5的成键主要来自于Cu原子d,p轨道与Sn原子p杂化,而Ni原子d轨道与Sn原子p轨道的强烈杂化作用是Ni3Sn4成键的主要原因.     

Microstructure evolution in Cu pillar/eutectic SnPb solder system during isothermal annealing

The reaction between Cu pillar and eutectic SnPb solder during isothermal annealing was studied systematically. Intermetallic compounds (IMCs), such as Cu₆Sn₅ and Cu₃Sn, were formed in between Cu and SnThe parabolic rate law was observed on IMC formation, which indicated that the growth of IMCs was controlled by atomic diffusion (a diffusion-limited process). Annealing at 165 °C for 160 h decreased the growth rate of Cu₆Sn₅, and at the same time increased the growth rate of Cu₃Sn. This was when Sn in solder was exhausted completely. The activation energies for the growth of Cu₃Sn and Cu₆Sn₅ were measured to be 1.77 eV and 0.72 eV, respectively. The Kirkendall void that formed at the interface between Cu pillar and solder obeyed the parabolic rate law. The growth rate of the Kirkendall void increased when the Sn in solder was consumed in its entirety.     

Nanomechanical characterization of Sn–Ag–Cu/Cu joints—Part 1: Young’s modulus,hardness and deformation mechanisms as a function of temperature

Nanoindentation has been used at room and elevated temperature to measure the spatial distribution of mechanical properties within Pb-free solder ball joints. The hardness, Young’s modulus and creep behaviour of the phases formed in a Sn–Ag–Cu/Cu solder joint have been characterized at temperatures from 25 to 175 °C. The hardness and Young’s modulus of Cu₆Sn₅ and Cu₃Sn had a weak dependence on temperature, while the hardness and modulus of primary β-Sn, eutectic regions and electroplated Cu were sensitive to temperature. Nanoindentation was able to detect both mechanical anisotropy in Cu₆Sn₅ and the sluggish η′ → η phase transformation at 150–175 °C. In a second part of this study, Pb-free solder creep behaviour has been investigated by nanoindentation and compared with Pb-free creep behaviour models from the literature. A two-dimensional finite-element analysis of solder nanoindentation creep has been used to compare creep measurement methods, and the insights from this analysis can be then implemented in commercial finite-element codes for creep behaviour prediction at the microscale in microelectronic solder joints.     

Microstructural evolution of intermetallic compounds in Sn–3.5Ag–X (X = 0, 0.75Ni, 1.0Zn and 1.5In)/Cu solder joints during liquid aging

In this paper, the microstructural evolution of IMCs in Sn–3.5Ag–X (X = 0, 0.75Ni, 1.0Zn, 1.5In)/Cu solder joints and their growth mechanisms during liquid aging were investigated by microstructural observations and phase analysis. The results show that two-phase (Ni₃Sn₄ and Cu₆Sn) IMC layers formed in Sn–3.5Ag–0.75Ni/Cu solder joints during their initial liquid aging stage (in the first 8 min). While after a long period of liquid aging, due to the phase transformation of the IMC layer (from Ni₃Sn₄ and Cu₆Sn phases to a (Cu, Ni)₆Sn₅ phase), the rate of growth of the IMC layer in Sn–3.5Ag–0.75Ni/Cu solder joints decreased. The two Cu₆Sn₅ and Cu₅Zn₈ phases formed in Sn–3.5Ag–1.0Zn/Cu solder joints during the initial liquid aging stage and the rate of growth of the IMC layers is close to that of the IMC layer in Sn–3.5Ag/Cu solder joints. However, the phase transformation of the two phases into a Cu–Zn–Sn phase speeded up the growth of the IMC layer. The addition of In to Sn–3.5Ag solder alloy resulted in Cu₆(Sn_x,In_1?x)₅ phase which speeded up the growth of the IMC layer in Sn–3.5Ag–1.5In/Cu solder joint.     

Bismuth segregation enhances intermetallic compound growth in SnBi/Cu microelectronic interconnect

There was a sudden increase of intermetallic compound (IMC) Cu₆Sn₅ growth rate in the eutectic Sn58wt. %Bi/Cu joint during aging process. With aging time increasing, Bi accumulated at the Cu₃Sn/Cu interface and gradually induced the fracture mode of the joint to change from ductile to brittle one along this interface. Bi segregation enhanced IMC Cu₆Sn₅ growth by means of promoting the interfacial reaction at Cu₃Sn/Cu interface, which was concluded from IMCs (Cu₆Sn₅ and Cu₃Sn) growth behavior for pure Sn/Cu and Sn10wt. %Bi/Cu interconnects at the same temperature.     

Microstructural and mechanical analysis on Cu–Sn intermetallic micro-joints under isothermal condition

This study focuses on the mechanism of phase transformation from Cu₆Sn₅ into Cu₃Sn and the homogenization process in full intermetallics (IMCs) micro-joints, which were prepared by soldering the initial Cu/Sn/Cu structure through high temperature storage in vacuum environment as the Transient Liquid Phase (TLP) process. From the microstructural observation by electron backscatter diffraction (EBSD), a mixture of IMCs phases (Cu₆Sn₅ and Cu₃Sn) has been found to constitute the sandwich-structured Cu/IMCs/Cu joints. With the dwell time increasing at 533 K, there were two layers of Cu₃Sn emerging from both sides of copper substrates with the depletion of Cu₆Sn₅ layer, toward merging each other in the IMCs interlayer. Then the Cu₃Sn grains with various sizes became more homogenous columnar crystallites. Meanwhile, some equiaxial ultra-fine grains accompanied with the Kirkendall voids, were found only in adjacent to the electroplated copper. In addition, a specific type of micropillar with the size ∼5 μm × 5 μm × 12 μm fabricated by focus ion beam (FIB) was used to carry out the mechanical testing by Nano-indentation, which confirmed that this type of joint is mechanically robust, regardless of its porous Cu₃Sn IMC interconnection.     

Effect of rare earth metal Ce addition to Sn-Ag solder on interfacial reactions with Cu substrate

The effect of adding a small amount of rare earth cerium (Ce) element to low Ag containing Sn-1wt%Ag Pb-free solder on its interfacial reactions with Cu substrate was investigated. The growth of intermetallic compounds (IMCs) between three Sn-1Ag-xCe solders with different Ce contents and a Cu substrate was studied and the results were compared to those obtained for the Ce-free Sn-1Ag/Cu systems. In the solid-state reactions of the Sn-1Ag(-xCe)/Cu solder joints, the two IMC layers, Cu₆Sn₅ and Cu₃Sn, grew as aging time increased. Compared to the Sn-1Ag/Cu joint, the growth of the Cu₆Sn₅ and Cu₃Sn layers was depressed for the Ce-containing Sn-1Ag-xCe/Cu joint. The addition of Ce to the Sn-Ag solder reduced the growth of the interfacial Cu-Sn IMCs and prevented the IMCs from spalling from the interface. The evenly-distributed Ce elements in the solder region blocked the diffusion of Sn atoms to the interface and retarded the growth of the interfacial IMC layer.     

The 260 °C phase equilibria of the Sn–Sb–Cu ternary system and interfacial reactions at the Sn–Sb/Cu joints

The isothermal section of the Sn–Sb–Cu ternary system at 260 °C has been determined in this study by experimental examination. Experimental results show no existence of ternary compounds in the Sn–Sb–Cu system. An extensive region of mutual solubility existing between the two binary isomorphous phases, Cu₃Sn and Cu₄Sb, was determined and labeled as δ. Intermetallic compounds (IMCs) Cu₂Sb, SbSn, and Cu₆Sn₅ are in equilibrium with the δ solid solution. Up to about 6.5 at.%Sb can dissolve in the Cu₆Sn₅ phase, and the solubility of Sn in the Cu₂Sb is approximately 6.2 at.%. Each of the Sb and SbSn phases has a limited solubility of Cu. Only one stoichiometric compound, Sb₂Sn₃, exists. Besides phase equilibria determination, the interfacial reactions between the Sn–Sb alloys and Cu substrates were investigated at 260 °C. Sb was observed to be present in the Cu₆Sn₅ and δ phases, and Sb did not form Sn–Sb IMCs in the interfacial reactions. Moreover, the addition of up to 7 wt% of Sb into Sn does not significantly affect the total thickness of IMC layers. It was found that the phase formations in the Sn–Sb/Cu couples are very similar to those in the Sn/Cu couples.     

Ni segregation in the interfacial (Cu,Ni)6Sn5 intermetallic layer of Sn-0.7Cu-0.05Ni/Cu ball grid array (BGA) joints

Ni segregation in the interfacial (Cu,Ni)₆Sn₅ intermetallic layer of Sn-0.7Cu-0.05Ni/Cu BGA solder joints was investigated by using synchrotron micro X-ray fluorescence (XRF) analysis and synchrotron X-ray diffraction (XRD). Compared to Sn-0.7Cu/Cu BGA joints, Ni containing solder show suppressed Cu₃Sn growth in both reflow and annealed conditions. In as-reflowed Sn-0.7Cu-0.05Ni/Cu BGA joints, Ni was relatively homogenously distributed within interfacial (Cu,Ni)₆Sn₅. During subsequent annealing, the diffusion of Ni in Cu₆Sn₅ was limited and it remained concentrated adjacent the Cu substrate where it contributes to the suppression of Cu₃Sn formation at the interface between the Cu substrate and Cu₆Sn₅ intermetallics.